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Discussion Starter · #1 · (Edited)


i have a standard Autozone/Duralast 5-year battery, whatever was stock for '90 Mustang GT. The car has 12,000 miles on it and the battery is almost 7 years old.

there have been a few slight hard/cold starts lately, so i went to Autozone and they did the parking lot test, it said bad battery. i can limp it a little longer, but i'd rather replace it.

the question is regarding idle, my headlights and dash lights are dim. this used to only happen if i had the heater or both footbox blowers blasting. i am surprised this would happen if i have a Powermaster alternator and non-HEI setup. the Voltmeter is always at 14V, maybe a little under 12V if i am at the stoplight with accessories blowing.

will a better battery such as an Optima really help me? the ads all talk about "cold cranking power", but starting is never a problem. nor is blasting the radio during tailgating and the engine not running

dim headlights at idle are not the end of the world, but if +$50 for an Optima battery will solve that problem i will Shirley spend it.

:icon22:
 

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You have two separate issues.

Dim lights and 12V are a result of low alternator output in relation to the electrical load requirement from the vehicle. Usually caused by too low alternator RPM using under drive pulleys.

A "good" stock capacity battery has enough CC amps to start the car. The dim lights and 12V scenario at idle will play out with a larger capacity battery as well.

Greg
 

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Discussion Starter · #3 ·
hi greg, i do have underdrive pulleys. i have so much power now i doubt the underdrive pulleys are making a dent, and i wonder if i should put the stock ones back on. i even still have the old length belt.

i think i will spring for the Optima battery as long as it fits in the tray.

there are three kinds, yellow red and blue. the blue is marine, so it's between yellow and red. will the basic red Optima do?
 

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Go back to the stock pulleys, use a red top and you can move into the light, so to speak. :)

Greg
 

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Not to muddy the waters, but are you running a stock 1990 mustang alternator (2G)? On my 88 mustang, I had many reliability issues with the stock alternator, including burning up a wiring harness and replacing the alternator many times (most under warrenty).

The 3G alternator, found on the next generation of ford vehicles (think mid to late 90's to 00's) was a huge improvement. The amp output at idle is much higher than the old 2G, and it is soooo much more reliable. Of course, your underdrive pulleys aren't helping, but even without underdrives I found the amp output at idle of the 2G marginal at best. The 3G upgrade is nice option to consider.
 

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Old battery

Eddie,

I have a 10 year old Red top Optima in my Roadster, never gives me second thoughts running off of a stock 5.0 alternator with underdrive pulleys. When it finally dies, I'm probably going to replace it with the same thing because it's been reliable.
When I'm at a stop light during evening driving, the volts drop to approx. 12.5 and the lights dim a bit . . . almost unnoticable. If that were an issue, I think my EFI would react to the low voltage and spit codes at me . . . it doesn't.

Doc :beerchug:
 

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Bhuff is right about the alternator. I had a 2G for a while but got tired of the lights dimming at idle. I put in a new 3G alternator and the voltage is always at 14V no matter what is on. Big improvement. I also have the red top Optima, no problems over three years so far.
 

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The 3G alternator is Ford's fix for the high power consumption at idle they have to deal with. It puts out close to 60 amps at idle, and 130 max.

Fuel injection on a factory setup runs 45-60 amps alone, which is why so many cars are in the 120+ class these days. Add a 1000 watt stereo setup and it sucks 40 amps all by itself. Lots of shops install a separate Optima just for the stereo now, cheaper than installing a 250 amp ambulance alternator.

Running a higher output alternator cures lots of low voltage issues. After 10-15 years, the voltage drop amounts to 1.5 - 2.0 volts - enough to cause sensor reading and computer problems, burn out lights prematurely, and create a power loss at higher rpms.

The better 3G alternator helps, the factory sized pulleys don't create a problem, and what's 6hp when you can get that by using synthetic motor oil? We are dealing with 8 pounds per hp compared to 14:1, the light weight car is already a huge advantage,.

Remember, they sell stuff because people will buy it, not because it really does something you actually need. Underdrive systems are for strip and track cars that run above 3,000 rpm 85% of the time. Not street cruisers or daily drivers.

I'd get a house brand AGM glass mat battery in the 800CCA range and call it good. You'll likely get a longer warranty, more power, and it will cost less money, plus you get coverage in a lot more places. It's a commodity product, get your money's worth. I've tried them both, and Optima is really just coasting on their reputation now that the industry has caught up.
 

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Is the Powermaster alternator a 1 wire? If it is, they don't normally start to charge until about 1000RPM. A Ford 3G will charge even at idle, as long as there aren't too many accessories running.
 

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The red topped battery will be just fine. You don't have much of a load compared to a factory car off the lot.
 

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2-g alternator,underdrive pullys, reg-sized battery(1000cc)here. No radio,power seats,or no power windows,ect, and all is well-
hth
Butch
 

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just thoughts...
http://www.summitracing.com/parts/dui-5575b/overview/ using this mounted on top of the passenger foot-box. Less weight and short cable runs, but its good to use a battery tender on it when sitting any length of time. There a larger ones that would fit that area too.

RJM Injection Tech — Alternators

Bought a 160 amp model. $130 New alternator, $10 pulley, $20 harness, $45 charge cable. adds up but a nice setup
RJM Injection Tech — Alternator Accessories

The rebuilt GM mid 70's alternator that I converted to 1 wire was not up to the task of the Powerjection, electric fans, electric power steering, lights....


$109 for a Valucraft rebuilt makes the new above look better.
Valucraft/Alternator (7734-6-11) | 1994 Ford Mustang 8 Cylinders T 5.0L SFI HO | AutoZone.com

RJM and Breeze sells a 90 amp model.
 

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I have a 2G alternator and a red top battery in the roadster, I dont charge well in traffic with the lights.

A fully charged red top open circuit should read 12.9 new. Im lucky if I can read 12.7 in the roadsterafter a 12 hour off period. The roadster battery is 9 years old

My Jeep wrangler optima (2 years old) reads 12.9V after 12 Hours sitting.

Thiis weekend the roadsted is getting a 3G alternator. I will let you know my result.

Keeping the battery in the trunk results in longer life.

Tierod...Fuel injection is only a couple of amperes. Sixty amperes ao 12 Volts is 720 watts! Your ECU bux would be GLOWING!
 

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I too am having problems, mine seem to surface when I turn the fan on my FFR supplied one. My volt meter goes to low 12v from low 13v. Seems that a new alt will help.

I am still new at tuning but, I do know that there is more to this concept than how much draw the ECU has on the electrical system. On the EFI side, the battery voltage does have an affect on how the injectors operate. There is a table called Inj offset vs Batt voltage, looks like this:

15.9375 0.7500
14.0000 0.8125
13.0000 0.9375
12.0000 1.0938
11.0000 1.2500
10.0000 1.4375

So you can see there can be a difference on the way the EFI system responds in relation to the injectors firing based upon Batt voltage.

For Eddie and the rest of the carb guys naturally this doesn't apply.
 

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That looks like the ford table for the A9L.
 

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I run a stock Ford 3G with under drive pulleys at 900 rpm idle speed. I can run the AC on max fan, BIG engine fan running, head lights on, and the alternator output is above 14V at idle with no dimming.

3G's rock.

Greg
 

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A couple of thoughts;
1- What GregM said in his first and second posts.
2-underdrive pulleys have a major effect at idle.Since you have a 'little' time to play with, I'd put stock pulleys back on and see the result.
3- I'd probably buy a replacement battery the same as you have especially since you stated that you have never had a starting problem w/ it.
4-Most (I would say all but could be caught out being too inclusive) modern cars have both the temp and battery gauges very very damped so owners don't clog the telephones w/ questions. IE: you know how you can watch your FFR temp gauge move up and down as the temp rises at idle and then the fan comes on? Notice you never see the needle move in your daily driver? It's damped and that needle won't move til about 30 seconds before the steam starts showing. Same w/ the volt or battery gauge. The few current cars that have one usually have a real wide green area and many have no numbers at all. My point is that you FFR gauge moves a lot compared to a daily current car and, as long as it is doing the same it did last week, don't worry about it much.
 

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Discussion Starter · #19 ·
http://www.summitracing.com/search/...e=100&SortBy=DisplayPrice&SortOrder=Ascending

okay so

deep cycle - starting - deep cycle/starting

:wacko: :wacko: :wacko:

this one came up for 1970 Mustang:

http://www.summitracing.com/parts/ult-9003-151/overview/make/ford/model/mustang/year/1970

the height says Height (in): 7.625 in.. my current battery is 6" high, i need to sort if that 7.625" includes the terminals, if not, the Optima may not fit, and i'll have to get a Duralast Gold battery.

they didn't have this Optima battery in stock at any local store for me to measure.
 
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